This invention relates to constant velocity universal joints of the type comprising spherically engaging inner and outer members, coupled together by a plurality of balls which engage arcuate meridian race grooves in the members. More particularly, this invention relates to apparatus adapted for grinding the race grooves of the spherically shaped inner member, which is often referred to as the inner race of a constant velocity universal joint of the Rzeppa type, as well known in this art. In the standard Rzeppa joint, adjacent meridian race grooves are ground about a common point, or center.
It has been determined that offsetting the centers of adjacent inner race grooves balances end thrust, and thus provides for enhanced high speed performance over the standard Rzeppa type universal joint. Thus, in U.S. Pat. No. 2,875,600, Miller discloses a pair of alternate offset centers about which the meridian race grooves of an inner race are ground.
A significant disadvantage has been realized, however, in the manufacture of Miller's inner race member. Machining alternate offset grooves has required grinding each groove about the spherical surface of the inner race on a one-at-a-time basis. This has been due to the Rzeppa joint's inherent possession of an even number (generally six) of equally spaced meridian race grooves, each groove having an opposing counterpart groove spaced exactly 180.degree. therefrom. The offset center geometry results in all such opposing pairs of grooves having to necessarily be ground about offset centers.
As fixtures employed in the grinding of standard Rzeppa type inner race grooves grind pairs of oppositely positioned grooves in a single cutting operation, the principal drawback of prior art devices for grinding alternate offset grooves is thus the lack of speed realized by virtue of the limitation of grinding only one groove at a time.